JPS6055325A - Correcting device of uneven illuminance in variable magnification copying machine - Google Patents

Abstract

PURPOSE:To correct uneven illuminance on the photosensitive body of a slit exposure type variable magnification copying machine in which magnification is varied by moving a lens in the optical-axis direction of an optical path precisely through simple constitution. CONSTITUTION:A correcting plate 11 which shields part of both ends of the optical path between the surface of an original at an exposure optical system and the lens 8 is provided at both breadthwise sides of the optical path. Consequently, the angle of incidence of luminous flux cut off by the correcting plate 11 to the lens 8 decreases according to the distance from the outermost point A of a slit on the original to the center to reduce the width of a shade appearing on the lens, and the luminous flux is cut off only by a part of the correcting plate 11 at a point B, so the width Wb of the shade is further reduced. For the purpose, the shape and size of the correcting plate 11 and its insertion position for every magnification are so predetermined that the ratio of the area of the shade on the lens to the area of an entrance pupil, may be equivalent to the ratio of the uneven illuminance in the longitudinal direction of the slit on the photosensitive body, thereby correcting uneven illuminance on the photosensitive body in the lengthwise direction of the slit.

Description

TECHNICAL FIELD The present invention relates to an apparatus for correcting illuminance unevenness in the longitudinal direction of a slit in a variable magnification copying machine of a slit exposure type that changes magnification by moving a lens in the optical axis direction of an optical path.

As shown in FIG. 1, the exposure system of a prior art electrophotographic copying machine is such that a document 3 placed on a contact glass 2 provided on the top plate of a copying machine body 1 is irradiated with a slit by a light source 4. The reflected light flux is reflected by a first mirror 5 that moves at a constant speed V together with the light source 4, a second mirror 6 and a third mirror 7 that move at the same speed, and is reflected by a lens 8 and a fourth mirror 9. A slit FF optical system is often used in which an image is formed on the photoreceptor drum 10 rotating at a circumferential speed V for exposure.

In order to perform variable magnification copying with this Koui optical system, - Lens 8, which was at the position shown by the solid line during full-scale copying, is moved to the image side as shown by the chain line 8' during reduction, and by the chain line 8 when enlarging. After the second and sixth mirrors 6.7 are integrally moved away from the lens 8 to positions 6/, y/, for example, the circumferential speed of the photosensitive drum 10 is V no ma\
Then, the light source 4 and the first mirror 5 are moved to the second and sixth mirrors at a speed of V/m.
Exposure scanning is performed by synchronizing the mirrors 6.7 at a speed of 772 m and moving in the same direction. Note that m is a magnification.

Conventionally, the standard for placing the document 3 on the contact glass 2 was often a one-sided standard in which the front edge of the document was aligned with the front edge of the contact glass 2, but with recent variable-magnification copiers, it is possible to place the original 3 on the contact glass 2 only by reducing the size. In addition, magnification variable power is also required, and the number of types of variable magnification increases, and in the case of one-sided reference, it is necessary to displace the lens not only in the direction of the optical axis according to the variable magnification, but also in a direction perpendicular to it, and the lens Since the displacement mechanism becomes complicated, a center reference has been adopted in which the document is placed so that the center line of the width in the direction perpendicular to the scanning direction of the document is aligned with the center line of the contact glass. In this case, the lens only needs to be moved in the direction of its optical axis when changing magnification, and the lens displacement mechanism becomes relatively simple.

FIG. 2 is a developed view of a plane including the slit direction of the optical path and the optical axis direction of the optical path of the optical system shown in FIG.

As mentioned above, during reduction, the lens 8 moves on the optical axis from the position 8 when it is at the same magnification to a position farther from the original document holder, for example, 8'.
When enlarging, on the contrary, it is displaced to a position closer to the document surface 6, for example, to a position of 8''.

Now, it is known that lenses have a cos fourth law, and the amount of light at the imaging plane decreases in proportion to eO8', the incident angle with respect to the lens optical axis, and the peripheral light meter of the screen decreases.

In FIG. 2, both ends A in the longitudinal direction of the slit on the original 3,
The angle of incidence of A' on the lens 8 is smaller than the angle of incidence θ at the same magnification when it is reduced, and becomes sharper when it is enlarged. Therefore,
When the luminance distribution in the longitudinal direction of the illumination lamp 4 is corrected in proportion to [1] so that the light intensity distribution in the longitudinal direction of the slit on the photoreceptor 10 becomes flat at the same magnification, the light intensity on the original illuminated by this light source is The light intensity distribution of the slit on the photoreceptor is
As shown in the figure, the central portion is the same as when the magnification is the same, but when the image is reduced, the closer it is to both ends, the greater the amount of light is. Conversely, when enlarged, the closer it is to both ends, the more the amount of light is decreased.

If the reference for placing the original on the contact glass is one-sided, the lens is moved away from the original and at the same time toward the reference edge during reduction, so that the image that comes out from the edge of the image on the reference edge side is moved toward the reference edge. Although the angle of incidence of light on the lens is smaller than when the magnification is the same, the angle of incidence of light on the lens from the opposite end does not change much. Therefore, if the brightness distribution of the light source lamp is corrected so that the light intensity distribution in the longitudinal direction of the slit on the photoconductor becomes flat when the magnification is the same, it is possible to The light intensity increases as it approaches the paper reference (which is the opposite of the document placement reference), and the light intensity distribution becomes almost flat on the opposite side. Therefore, as a correction device for this illuminance unevenness, Japanese Patent Application Laid-Open No. 53-91728 proposes a device that blocks a part of the light flux from the reference end side on the outside of the optical path toward the optical axis between the document surface and the lens. A device in which a member is inserted is shown, but if the document placement reference is the center line, the amount of light increases from the center to both ends, so it cannot be corrected using this method.

Purpose The present invention addresses the above-mentioned actual situation regarding the correction of illuminance unevenness in the longitudinal direction of the slit on the photoreceptor when changing the magnification in a variable magnification copying machine in which the document placement reference is the central reference, and has a simple configuration. An object of the present invention is to provide a device that can accurately correct illuminance unevenness on a photoreceptor.

Configuration The present invention will be described in detail below based on drawings showing embodiments.

The present invention is capable of shielding a portion of both ends of the optical path on both sides in the width direction of the optical path between the document surface and the lens in the exposure optical system of a variable magnification copying machine in which the document placement reference is the center reference. A correction plate is provided, and the two on both sides of the correction plate can be set at preset positions depending on the magnification, and at that position, a part of the light flux from each position of the original sliver σ is blocked and a part of the light beam from each position is blocked and the two are placed on the lens. The position of the shadow, and the shape and dimensions of the member are determined so that the ratio of the area of the shadow cast on the lens to the entrance pupil of the lens corresponds to the ratio of uneven illuminance at the corresponding portion on the surface of the photoreceptor.

FIG. 4 is a diagram showing an embodiment of the present invention, and shows the position 8 of the lens 8 in FIG. 2 at the same magnification and the original m Light rays entering the lens 8 are shown from points A and A' (see Fig. 2) at the outermost ends of the upper slit. A correction plate 11 is provided on both sides of the optical path.
A sector gear is provided on the opposite side of the bracket from the correction plate, and meshes with a screw shaft 15 driven by a motor 14. The screws of the screw shaft 15 are opposite to each other on the left and right sides of the figure, and by turning them, the left and right correction plates 11 simultaneously rotate in opposite directions about the shaft 12, and the screws are set in advance for each magnification. position and blocks part of the luminous flux.

The operation of this device will be explained with reference to FIG. 5. A part of the light beam emitted from the outermost point A of the slit on the document
The light is blocked by and casts a shadow with a width of Wa on the lens. As the point approaches the center from point A, the angle of incidence of the light beam from that point that is blocked by the correction plate 11 on the lens 8 becomes smaller, and the width of the shadow falling on the lens becomes smaller. Since only a part of 11 is covered by the luminous flux, the width of the shadow is
b becomes even smaller. In this way, the width of the shadow increases as it approaches both ends of the slit of the document, and there is no shadow in a certain area in the center.

In this way, the amount of light reaching the corresponding point of the slit on the photoreceptor decreases by the ratio of the area of the entrance pupil of the shadow surface on the lens to the area of the entrance pupil of the clear lens. The correction plate 11 is adjusted so that the ratio of
If the shape, dimensions, and insertion position at each magnification are determined in advance, uneven illuminance on the photoreceptor in the longitudinal direction of the slit can be corrected.

In the above embodiment, the luminance distribution in the longitudinal direction of the light source is corrected so that the illuminance distribution on the photoreceptor becomes flat when the magnification is the same, so it is corrected by the above correction plate when reducing the size. Deficiencies are not corrected. However, since the luminous flux is not blocked at the same magnification, which is the most frequently used mode, the illumination efficiency is high.

In order to accurately correct uneven illuminance through enlargement, same magnification, and reduction, the brightness distribution of the light source lamp should be corrected so that the illuminance distribution on the photoreceptor during enlargement is flat, and the correction plate should be used to adjust the luminous flux even when the same magnification is performed. Just insert it inside.

Effects As described above, according to the present invention, uneven illuminance on the photoreceptor can be easily and accurately corrected with a simple RIFI configuration, and adjustment is also easy.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view showing an example of an optical system to which the present invention is applied, Fig. 2 is a plan view showing the optical path expanded, and Fig. 3 is a longitudinal sectional view of the slit on the photoreceptor in the optical system. FIG. 4 is a curve diagram showing an example of illuminance distribution during reduction, same magnification, and enlargement, FIG. 4 is a plan view showing an embodiment of the present invention, and FIG. 5 is a schematic diagram illustrating its operation. 2...Contact glass 6...Original 8...Lens 11...Correction plate 1) Agent Patent attorney Takehisa Ito: ;+---', 1 4th 闗( -164-

Claims (1)

[Claims] This is a slit exposure method in which the standard for placing the original on the contact glass is the center of the width in the direction perpendicular to the original scanning direction, and magnification is changed by moving the aperture lens in the optical axis direction of the optical path. In a photoreceptor illuminance unevenness correction device in the longitudinal direction of a slit in a variable magnification copying machine, correction plates capable of blocking a part of both ends of the optical path are provided on both sides of the optical path between the document surface and the lens in the width direction. The two correction plates on both sides can be set at the same time in preset positions according to the magnification, and at that position they block part of the light flux from each position of the slit on the document, reducing the shadows cast on the lens. The illuminance unevenness characterized in that the position and the shape and dimensions of the correction plate are determined such that the ratio of the area to the area of the entrance pupil of the lens corresponds to the ratio of the illuminance unevenness of the corresponding part on the surface of the photoreceptor. correction device.